Pneumatic follow-up pressure regulator



July 31, 1951 H. J. woos PNEUMATIC FOLLOW-UP PRESSURE REGULATOR Filed July 24, 1944 Six neuter: #0445? J W000 (Ittorneg- Patented July 31, 195T UNITED PATENT om PNEUMATIG FOLLOW-UP PRESSURE REGULATOR Homer 1. 'Wood, Los Angeles, Galifl, assign-or to The Garrett Corporation, Airesearch. Manufacturing Company division, LosAngeles, Califl, a corporation or California I Application 'July'Z I, 1944, Serial No. 546,353 g .17 Claims.

My invention 'relatestome'an's for controlling the pressure of air in pressurized cabins of aircraft, and. relates in particular to: a simple con trol mechanism having parts responsive to absolute cabin pressure and. also to the pressure differential: between the cabin. interior and exterior to maintain predetermined pressures in the cabin for diflerent flight altitudes.

It is an object of theinvention to provide a control device for pressurized cabins having an element which responds only to changes in pressure or the: air within the aircraft cabin, and a device which responds to changes in. air pres sure inside and outside the cabin, with means whereby the controlling efiect derived from both of these responsive elements; are utilized to control the pressure of air within. the cabin.

A. iurther object of the invention is to provide a control device having a cabin pressure control valve which is opened and closed in accordance with changes in air pressure,- andmeans whereby a flow of air under pressure is delivered to the controlling means of theair valve, this flow of air under pressure being derived from two separate sources, one of which is controlled by changes in absolute pressure within the cabin, and the other of which is controlled. by changes in pressure differential between the interior and exterior of the cabin.

A further object of the invention. is to provide a means for regulatingv pressure in anaircraft cabin having an outflow valve operated by pressure differential between the cabin and the outside atmosphere, the operation of said outflow valve being controlled by two valves disposed in parallel, one of these control valves being sensitive to cabin absolute pressure while the other is sensitive to the existing difierential pressure between the cabin interior and the cabin exterior.

A further object is to provide a control device whereby pressure sensitive means are subjected to cabin pressure modulated by passage through a feeder orifice, thereby producing a pneumatically etfectuated proportional control which minimizes the hunting tendency found in control devices of this general character.

A further object of the invention is to provide a control valve-mechanism having air valves of simple form, the outlets of which are connected to the air chamber of the main cabin air valve, and the inlets of which are connected to the cabin interior or selected source of air pressure through a flow controlling orifice.

Further obiects and advantages of the invention will be brought out the following part of the specification.

. "'2 Referring to the drawings whichv are for illustrative purposes 011151,.

, Fig; 1' is a schematic view showing a manner of use of one embodiment of my invention i'n'an aircraftcabinJ Fig; 2 is an enlarged sectional view showing'the control device of Fig: 1".

In-Fig: "1 T- have" shown an aircraft cabin -f0 into which air under pressure is f'edby a blower H. In the-wall I? o thecabin Hi there 'is-an air outlet opening *3 with a valve t4 eooperates to control the rate-oi discharge of air from the cabin l -lt ini-suclrrelationite the how of into-the .cahin. from. the blower that predetermined pressures 82138 maintained. Avalve operating-means ti -controlled bya con.- trol pleuice I161; actuates; the valve vHl. As shown in 2, the valve lit is .formed upona stem. {l1 ha n a rie ...or rms 133m c mm on of external. ambient .fiight pressure to .a chamber [9 formed on the face of a diaphragm or movable wall 20" whihis'i'ar from the valve. i l. 'This chamber l'9is formed "bya sheIlTl' whichis se cured-"to a Supporting structure defining a chamber 23' on the opposite side of the movable wallQU. -The'structure 22 has a tubular portion 2ii'--surrounding a portion of the stem H- and having therein bearings- 25 to support the stem 14- for axial sliding: movement. At the-lower endof the supportmgtstrncture .22 there is an annular walllfi; forming a chamber 21,.the lower partof which is open. toreceive the upper part of thewalvei lr In the valve there areopenings is throu h. which. re r communication be. tweenthe up erand. lower face of the valve H is accomplishedf The chamber 23 has aniiair bleed connectionwith "the atmosphereexternal of the cabin, coh's'istingofa small, passage 30 -in t'he stem r1, connecting the'chamb'erfl toithe pas sage- ['8 which communicates-with the exterior through the lower end-of the stem below the The chamber is connected with air valves 7 and 32- through'duetsf33=and 34t The vatve Bit has valve passages 35,. which communicate throughacompartmentfifi with. a, duct 3 having an inl et. 38 communicating with the interior of thecabin The duct el -is provided. with a flow controlling orifice iiqithrough. which cabin. .air may 'fiow' The valve'si has valve passages 40 which communicate through 'a' chamber H with the duct} 31. "Onejwall "oi the chamber if is f'b'mn'ed bya -diaphr'agm Manda wall it is provided so as todefinea chamber-M on the sidecf thediaphragnr I?! opposite the chamber; this chamber '1 communicating through a'passage 45 with ambient air pressure. The diaphragm 42 is connected to a valve closure 46 which is urged by an adjustable spring 41 toward a position to close the passage 4|] of the valve 32. In the compartment 36 there is an evacuated capsule or aneroid 48 supported by an adjustment screw 49 and being connected to a valve closure 50 which closes the valve passages 35 of the valve 3| in response to expansion of the aneroid 48.

In the operation of the control device, air under pressure passes through the duct 31 into the compartment 36, and the chamber 4|. The pressure of this air produces collapsation of the aneroid 48 so as to open the valve passages 35 of the valve 3| in keeping with the absolute pressure of air in the cabin ID. The pressure of air in the chamber 4|, derived from the cabin, and the pressure of air in the chamber 44, derived from ambient flight atmosphere, produces a pressure differential on the diaphragm 42 which moves the same downward so as to open the passages 40 of the valve 32. The flows of air from the valves 3| and 32 pass through the ducts 34 and 33 into the chamber 23 of the valve actuating unit [5. In view of the lower pressure existing in the chamber l9 under flight conditions, due to its connection through the passage [8 with ambient flight pressure, the diaphragm is moved upward against the force of a spring 55 which exerts a closing movement against the upper end of the valve stem II, the result bein that the diaphragm 20is lifted and the stem transmits a lifting movement to the valve |4 so as to increase the effective size of the air outlet opening l3, in response to an increase in pressure in the cabin, and also in response to an increase in pressure differential between the cabin air and the atmospheric pressure existing out 'side the cabin. Also, a reduction in cabin pressure and a reduction in the differential pressure existing between cabin air and ambient flight air outside the cabin will reduce the flow of air into the chamber 23, so that there will be a reduction in pressure in the chamber 23. owing to leakage therefrom through the bleeder passage 30, with the result that there will be a closing movement of the valve |4. When a prescribed differential between cabin pressure and ambient flight pressure is reached, the differential control 32 will replace the aneroid control 3|. A characteristic ofthedevice is that pressure in the compartment 36 and in the chamber 4| is modified from cabin pressure as the result of the interposing of the orifice 39 in the path of air flow, and is less than cabin pressure, but varies in accordance with cabin pressure and also thechanges in the rates of flow through the orifices 30 and 39. The following example of the mode of operation of the device refers to specific pressure ranges, but it will be understood that either or both of the isobaric and differential pressure controls can proached, the bellows 48 starts to expand to close ;-:-1

the valve 50, tending tocut off communication 4 of modified cabin pressure to the diaphragm 20. The spring 55 then acts to partially close the valve I4 since the pressure in the chamber 23 tends to leak to atmosphere through the passage |8. The bellows 48 and the valve .50 act to maintain cabin pressure constant until an altitude of 30,000 feet (for example) is approached. At this time the reduction in pressure in the compartment results in an expansion of the bellows 48 which will substantially close the valve 50 and modified cabin pressure acting on the upper side of the diaphragm 42 exceeds the combined force of the outside atmospheric pressure and the force of the spring 41 acting on the lower side of the diaphragm 42, and as a result, the valve 46 is opened to transmit pressure through the duct 33 to the underside of the diaphragm 20' to cause opening of the exhaust valve I4. The diaphragm 42'and the valve 46 act to maintain a constant differential of cabin pressure over atmospheric pressure for altitudes above 30,000 feet.

I claim as my invention:

1. In a control for a pressure cabin, the combination of: a wall forming a valve opening connecting the cabin interior with the exterior; a valve for said opening, said valve having a projecting stem with a passage therethrough communicating with the exterior of the cabin; a chamber member having a movable wall connected to said stem, said chamber member forming a first air chamber adjacent the face of said movable wall far from said valve and communicating with said passage, and forming a second chambercommunicating with the face of said movable wall near said valve, there being a bleeder port in said stem connecting said second chamber with said passage of said stem; a pair of air valves each having its outlet connected to said second chamber and-the inlet thereof connectd to a duct which communicates with the interior of the cabin through an air flow controlling orifice; means responsive to changes in absolute pressure in said cabin toactuate one of said air valves; and means responsive to changes in pressure differential between the interior and exterior of said cabin for actuating the other of said air valves, whereby the flow of air from the cabin interior into said second chamber will be determined by said air valves.

2. In a control for a pressure cabin, the combination of: a wall forming a valve opening connecting the cabin interior with the exterior; a valve for said opening, said valve having a projectlng stem witha passage therethrough communicating with the exterior of the cabin; a chamber member having a movable wall connected to'said stem, said :chambermember formin a first air chamber adjacent the face of said movable wall far from said valve and communicating with said passage, and forming a second chamber communicating with the face of said movable wall near said valve, there being a bleeder passage connecting said second chamber with a zone of"pressure lower than the pressure in said second chamber; a pair of air valves each having its outlet connected to said second chamber and the inlet thereof-connected to a duct-which communicates with'the interior of the cabinthrough an air :flow controlling orifice; means'responsive to changes in absolute pressure in said cabin to actuate one of said air valves; and means responsive to. changes in pressure of differential between the interior and exterior of said cabin for actuating the other oflsaid air vaves, whereby the now or air from the. cabin mte-rior into said second chamber" will be determined by said air valves 7 a I 3. Ina control for a pressure: cabin-,the-comb-ihation of: a wall forming a valve: opening connecting the cabin interior with the exterior; a valve for said opening, said valve having apro iecti ng stem with a passage therethrong-h cornmunica-ting with the exterior of the cabin; a chamber member having a movable wall con-- nected to said stem, said chamber member to ming a first air chamber adjacent the face of said movable wall far trom'sai'd valve and communicatin with: said passage; and forming a second chamber communicating with the face or said movable wall near said valve, there being a bleeder port in said stemconnecting said: second chamber with said passage or said stem; a pair of air valves, each having its outlet-connected: to said second chamber and the inlet thereof connected to the interior of the cabin; an aneroi d exposed to air pressure derived from the interior of the-cabin; means connectingthemovable art or said aneroi'd to one or said air valves soas to openthe same upon an increase air pressure in the cabin and means responsive to changespressure difierential between theinterior and exterior of said cabin for actuating the other or said air valves, whereby the flow of air from the cabin interior into said second chamber will be determined bysaid air valves.

4S In a control for apre'sstir'e cabin, the bination of: a wall forming a valve opening connectin the cabin interior theexterior; a valve for said opening, said valve having a project'ing stem with a passage therethroug-h communicating with the exterior of the cabin; a; chamber member having a movable wall connected' to said stem, said chamber memberforming a first air chamber adjacentthe face of said movable wall far from said valve and communicating with said passage, and forming asecond chamber communicating with the face of said movable wall near said valve, there bein a ble'eder passage connecting said second chamber with a zone of pressure lower than the pressure said second chamber; a pairoi air valves, having its outlet connected to said second ch 1 her and the inletthereof connected tothe imteri'or' of the cabin; ananeroid exposed to air pressure derived from the interior of the cabin; rhea-1 1s connecting the movable partof said aneroid to one of said air valves so as toopen the same upon an increase in air pressure the cabin; and means responsive to changes in pres 6 or air=.'valves-,- each havin its outlet connected to said second chamber and the inlet thereof connected to aduct which communicates with the interior of the cabin through an air flow controllingorifice; means responsive to changes absolute pressurein said cabin to actuate one of said air valves; a resiliently supported septum;- wall means forming chamberson the opposite sidesof saidseptum connected respectively to the-lrlterior'and the exterior of said cabin; means connecting said septum to the other of said air valves whereby movement of said septum in re sponse to an increase in air pressure difie'rential between the interior and the exterior of said cab in will open said other air valve, whereby the-flow of air from the cabin interior into said second chamber will be determined by said air valves; 6. In a control for a pressure cabin, the combination of: a wall forming a valve opening con necting the cabin interior with the exterior;- a valve for said opening, said valve having apro-- jecti-ng stem with apassage" therethrough coin-- munioati-ng with the exterior of the cabin; a chamber member having a movable wall connect'e'd to said stem, said chamber member formingafirst air chamber adjacent the face of said sure differential between the interior and exterior of said cabin for actuating the other of said air valves, whereby the how of air from the cabin interior into said second chamber will be determined by said air valves. I

5. In a control for a pressure cabin, theco-m bination of a wall forming a valve opening-con meeting the cabin interior with the exterior; "a valve for said opening, said valve having a projecting' stem with apassage therethrough commun-matin with the exterior of the cabin i a chamber member having a movable wall con nected to said stem, said. chamber member forming a first air chamber adjacent the face or said movable wall far from said valve and commitnicating with said passage, and..formi ng a second chamber communicating with the face of said movable wall near said valve, there being a bleeder port insaid stein: connecting said second chamber with said passage of said stem; ae-pair movable wall far from said valve and communicating with said passage, and forming a second chamber communicating with the face of said movable wall near said valve, there being a bleeder port in said stem connecting said second chamber with said passage of said stem; a pair of air valves, each having its outlet connected to said second chamber and the inlet thereof corrnected to the interior of the cabin; an aneroid exposed to air pressure derived from the interior of the cabin; means connecting the movable part of said aneroicl to one of said air valves so as to open the same upon an increase in air pressure in the cabin; a resiliently supported septum; wall; means forming chambers on the opposite sides of said. septum connected respectively to the interior and the exterior of said cabin; means connecting said septum to the other of said air valves whereby movement of said septum in response to an increase in air pressure differential between the interior and the exterior of said cabin will open said other air valve, whereby the now of air from the cabin interior into said second chamber will be determined by said air valves. a

7.- In a control for a pressure cabin, thecombination of: a wall forming a-valve openingcon necting the cabin interior with the exterior; a valve for said opening, said valve having a projecting stem with a passage therethroug-h com municating with the exterior of the cabiny-a chamber member havinga movable wall con-- nected to said stem said chamber member form ing a first air chamber adjacent the face oi said movable wall far from said valve anticommunicating with said passage, and torn-ling a second chamber communicating: with the face or said movable wall near said valve, there being a bleeder passage connecting said-second chainher with a z'o'ne of pressure lower than the pressure in said secondchamber; a pair of air valves, each having its outlet connected-to said second chamber and the inlet thereof connected t'0- the interior of the cabin; an aneroid exposed to air pressure derived from the" interior of the-cabin; means connectingthe movable part of said aneroid to one-of said air valves so as to open thesame upon an increase in air pressure in the cabin; a resiliently supported septum; wall means forming chambers on the opposite sides of said septum connected respectively to the interior and the exterior of said cabin; means connecting said septum to the other of said air valves whereby movement of said septum in response to an increase in air pressure differential between the interior and the exterior of said cabin will open said other air valve, whereby the flow of air from the cabin interior into said second chamber will be determined by said air valves.

8. In a control for a pressure cabin, the combination of: a wall forming a valve opening connecting the cabin interior with the exterior; a valve for said opening, said valve having a proecting stem with a passage therethrough communicating with the exterior of the cabin; a chamber member having a movable wall connected to said stem, said chamber member forming a first air chamber adjacent the face of said movable wall far from said valve and communicating with said passage, and forming a second chamber communicating with the face of said movable wall near said valve, there being a bleeder port in said stem connecting said second chamber with said passage of said stem; a pair of air valves, each having its outlet connected to said second chamber and the inlet thereof connected to the interior of the cabin; walls forming a compartment connected to the interior of the cabin through an air flow controlling orifice; an aneroid exposed to air pressure in said compartment derived from the interior of the cabin; means connecting the movable part of said aneroid to one of said air valves so as to open the same upon an increase in air pressure in the cabin; a resiliently supported septum; wall means forming chambers on the opposite sides of said septum connected respectively to the interior through an air fiow controlling orifice and the exterior of said cabin through duct means; means connecting said septum to the other of said air valves whereby movement of said septum in response to an increase in air pressure differential between the interior and the exterior of said cabin will open said other air valve, whereby the flow of air from the cabin interior into said second chamber will be determined by said air valves.

9. In a control for a pressure cabin, the combination of: a wall forming a valve opening connecting the cabin interior with the exterior; a valve in said opening; means comprising a chamber to receive air under pressure, said chamber being vented to a zone of lower pressure; a second chamber connected with a zone of lower pressure; means separating said chambers and operating in response to changes in the differential of pressures in said chambers for moving said valve; a pair of air valves each having its outlet connected with the first mentioned chamber and the inlet thereof comiected to a duct which communicates with the interior of the cabin through an air flow controlling orifice; means responsive to changes in absolute pressure in said cabin to actuate one of said air valves; and means responsive to changes in pressure differential between the interior and exterior of said cabin for actuating the other of said air valves, whereby the flow of air from the cabin interior into said first mentioned chamber will be determined by said air valves.

10. In a control for a pressure cabin, the combination of: a wall forming a valve opening connecting the cabin interior with the exterior; a

valve for said opening; means for controlling the position of said valve, said means comprising a chamber for receiving air under pressure, said chamber being vented to a zone of lower pressure; a second chamber connected with the exterior of the cabin; means separating said chambers and operating in response to changes in the differential of pressures in said chambers to move said valve; a pair of air valves each having its outlet connected to the first mentioned chamber and the inlet thereof connected to the interior of the cabin; an aneroid exposed to air pressure derived from the interior of the cabin; means connecting the movable part of said aneroid to one of said valves so as to open the same upon an increase in air pressure in the cabin; and means responsive to changes in pressure differential between the interior and the exterior of the cabin for actuating the other of said air valves, whereby the flow of air from the cabin interior into the first mentioned chamber will be determined by said air valves.

11. In a control for a pressure cabin, the combination of: a wall forming a valve opening connecting the cabin interior with the exterior; a valve for said opening; means for controlling the position of said valve, said means comprising a chamber for receiving air under pressure, said chamber being vented to a zone of lower pressure; a second chamber connected with the exterior of the cabin; means separating said chambers and operating in response to changes in the diiferential of pressures in said chambers to move said valve; a pair of air valves each having its outlet connected to the first mentioned chamber and the inlet thereof connected to a duct which communicates with the interior cabin through an air flow controlling orifice; means responsive to changes in absolute pressure in said cabin to actuate one of said air valves; a resiliently supported septum; wall means forming chambers on opposite sides of said septum connected respectively to the interior and the exterior of said cabin; means connecting said septum to the other of said air valves whereby movement of said septum in response to an increase in air pressure differential between the interior and the exterior of the cabin will open said other air valve, so that the flow of air from the cabin interior into the first mentioned chamber will be determined by said air valves.

12. In a control for a pressure cabin, the combination of: a wall forming a valve opening connecting the cabin interior with the exterior; a valve for said opening; means for controlling the position of said valve, said means comprising a chamber for receiving air under pressure, said chamber being vented to a zone of lower pressure; a second chamber connected with the exterior of the cabin; means separating said chambers and operating in response to changes in the differential of pressures in said chambers to move said valve; a pair of air valves each having its outlet connected to the first mentioned chamber and the inlet thereof connected to the interior of the cabin; an aneroid exposed to air pressure derived from the interior of the cabin; means connecting the movable part of said aneroid to one of said air valves so as to open the same upon an increase in air pressure in the cabin; a resiliently supported septum; wall means forming chambers on opposite sides of said sep tum connected respectively to the interior and the exterior of said cabin; means connecting said septum to the other of said air valves wherebyanovementpfisaid septum in response to" an in- ,crease in air pressure di-fi'erential between the interior andexteri-or of said cabinwill open said .other air valve so that'theflow of air from the cabin interior into the 'first'mentioned chamber will bedeterminedbyboth said air valves.

'13. In a control-for a pressure-cabin; the icombination of: a walri o'rming a valve'opening connecting the cabinirr terior with the exterior; a valve for said op ening; means for controlling the position of said 'va/lve; said means comprising a chamber for receiving air under pressure; said chamber being vented to a zone of lower pressure; a second chamber connected with the exterior of the cabin {means separating said chambers and operating in response to changes in't'he differential of pressures in said chambers to move said valve; a pair of air valves each having its outlet connected to the first mentioned chamber and the inlet thereof iccnpectedrtoethe interior of the cabin through an airflow .controlling oriflce; a. compartment forming part of said connection; an aneroid exposed to air pressure in said compartment derived from the interior cabin; means connecting the movable part of the aneroid to one of said air valves so as to open the same upon an increase in air pressure in the cabin; a resiliently supported septum; wall means forming chambers on opposite sides of said septum connected respectively to the interior of the cabin through said air flow controlling orifice, and to the exterior of the cabin through duct means; and means connecting said septum to the other of said air valves whereby movement of said septum in response to an increase in air pressure diiferential between the interior and the exterior of said cabin will open said other air valve, so that the flow of air from the cabin interior into the first mentioned chamber will be determined by said air valves.

14. In mechanism for controlling the pressure within an enclosure having an opening to the exterior thereof: a control pressure chamber, a flexible diaphragm, one side of said diaphragm being subjected to the pressure in said chamber; a valve positioned adjacent said valve opening and being movable to control the flow therethrough, there being means connecting said valve and said diaphragm so that movement of said diaphragm moves said valve; wall means defining a space on the side of said diaphragm opposite said pressure chamber and having a connection to atmosphere; spring means exerting a force against said diaphragm in a direction tending to close said valve; passage means adapted to connect said control pressure chamber with the enclosure; a second passage means of fixed crosssectional area adapted to connect said chamber with ambient atmosphere; and pilot valve means, including a differential pressure responsive device, subjected to atmospheric pressure and enclosure pressure on opposite sides thereof for controlling said first passage means.

15. In mechanism for controlling the pressure within an enclosure having an opening to the exterior thereof: enclosure pressure control means operable to control the pressure in said enclosure, including a movable pressure sensitive element, a fiow control valve operatively connected to said pressure sensitive element, spring means exerting a pressure against said pressure sensitive element in a direction tending to close said valve, means to connect one side of said pressure sensitive element to atmospheric pressure, and a control chamber on the opposite side of said pressure sensitive element; an outlet passage adapted to connect said control chamber with the exterior of said enclosure; a supply passage adapted to connect said-control chamber with the enclosure; and pilot valve means, including a differential pressure responsive device; subjected to atmospheric pressure and enclosure pressure on opposite sides thereof, for controlling said supply passage.

1 6. Mechanism for controlling the air pressure within an aircraft cabin, supplied with air under pressure and having anair' outlet, while permitting a continuous circulation of air through said cabin for ventilation thereof, comprising: means for modulatedcontrol of the outflow of air from said air outlet, including a movable pressure sensitive element having "an area on one side-subjected to ambientatrhospheric pressure; walls de fining a control pressure chamber, the other side of said pressure sensitive element being subjected to the pressure in said chamber; spring means urging the pressure sensitive element-in a direction to effect reduction'of airflow through-the outlet; outlet passagemean's; including a fixed bleed orifice, for the flow of air from said control chamber to atmosphere; inlet passage means connecting the cabin with said control chamber for the fiow of air from said cabin into said chamber; pilot valve means for controlling the pressure in the control chamber, said pilot valve means including a movable isobaric pilot valve member controlling the flow of air through the inlet passage means; an evacuated bellows having one end fixed and the other end movable and connected to said isobaric pilot valve member, said bellows being responsive to variations of pressure in the cabin for regulating the position of said pilot valve member so that the latter will permit a modulated flow of air through said passage means, which flow is varied in accordance with movements of said movable end of said bellows; a movable differential pilot valve member for controlling the flow of air through the inlet passage means; a spring urging said differential pilot valve member in the closing direction; and differential pressure responsive means connected to the differential pilot valve member, said differential pressure responsive means being subjected on one side to atmospheric pressure and subjected on the opposite side to cabin pressure so that said differential pressure responsive means is responsive to variations of pressure between that in the cabin and atmosphere for regulating the position of said diiferential pilot valve member so that the latter will permit a modulated flow of air through the inlet passage means, which flow is varied in accordance with movements of said difierential pressure responsive means.

17. Mechanism for controlling the air pressure within an airplane cabin, said cabin having an air outlet opening through which ventilation air may flow to the exterior, the combination including: a control pressure chamber; a pressure sensitive diaphragm, one side of said diaphragm being subjected to the pressure in said chamber; a cabin air flow control valve positioned adjacent said outlet opening of said cabin and being movable to control the rate of air flow therethrough, there being means connecting said valve and said diaphragm so that movement of said diaphragm moves said valve into different air flow controlling positions with respect to said outlet opening; wall means defining a space on the side of said diaphragm opposite said control pressure chamber and having an open connection to atmosphere; spring means exerting a force against said necting said control pressure chamber with am- -bient atmosphere; an isobaric control valve in said supply passage means movable into different positions for controlling the amount of air which may flow from said cabin to said control pressure chamber; an isobaric bellows connected to said isobaric control valve, there being means for exposing said isobaric bellows to be responsive to changes in cabin air pressure, said isobaric bellows being connected to said isobaric control valve to move said isobaric control valve when said isobaric bellows expands or contracts; a differential control valve in said supply passage means, said differential control valve being movable into different positions for controlling the amount of air which may flow from said cabin to said control pressure chamber; and diiTerential control means, there being means for expos- 12 mg one side of said differential control means to cabin air and the other side to atmospheric air, said differential control means being responsive to diiferentials in pressure between said cabin and atmosphere, said differential control means being connected to said differential control valve to move said differential valve when said differential control means moves.

HOMER J. WOOD.

REFERENCES CITED Schwein Dec. 18, 1945 Noxon Mar. 5, 1946 FOREIGN PATENTS Country Date Great Britain May 27, 1940 Number Number Certificate of Correction Patent N 0. 2,562,684

July 31, 1951 HOMER J. WOOD It is hereby certified that error appears in the printed specification of e above numbered patent requiring correction as follows:

Column 5, line'l, for vaves read wakes and that the said Letters "Patent should be read as corrected above, so that the same may conform to the record'of the case in the Patent Oflice.

Signed and sealed this 16th day of October, A. D. 1951.

THOMAS F. MURPHY, 

